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Laboratory and field measurements of the electrical charge carried by volcanic ash particles and observations of ash aggregates

Allan Fries1 , Eduardo Rossi1, Jonathan P. Merrison2, Jens Jacob Iversen2, Tatsushi Matsuyama3, Valentin Fréret-Lorgeril4, Jonathan Lemus1,5, Simon Thivet1, Carolina Diaz-Vecino1, Riccardo Simionato1,5, Simona Scollo6, Costanza Bonadonna1

  • Affiliations: 1Département des Sciences de la Terre, Université de Genève, Geneva, Switzerland; 2Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark; 3Department of Science and Engineering for Sustainable Innovation, Soka University, Tokyo, Japan; 4Laboratoire Magmas et Volcans, Université Clermont Auvergne, Clermont-Ferrand, France; 5Department of computer sciences, University of Geneva, Carouge, Switzerland; 6Istituto Nazione di Geofisica e Vulcanologia, Osservatorio Etneo, Catania, Italy 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 90

  • Programme No: 3.12.16

  • Theme 3 > Session 12

Abstract

Several mechanisms contribute to electrification during explosive volcanic eruptions, including fracto-emission from fragmentation and tribo-electrification from particle collisions. This electrification explains the occurrence of volcanic lightning and enhances aggregation by increasing electrostatic attraction and sticking efficiencies between ash particles. The resulting larger aggregates settle faster than individual particles, affecting sedimentation rates and particle residence time in the atmosphere. However, direct measurements of electrical charges on volcanic ash particles remain rare, limiting our understanding of how ash electrification influences aggregation. Additionally, laboratory experiments are needed to assess the impact of electrical charges on sticking efficiencies. This study presents a cost-effective, portable device designed to quantify the charge and fall velocity of individual volcanic ash particles and aggregates. Using a charge amplifier circuit and an Arduino microcontroller, the device records the very small voltages induced by charged particles crossing a Through-Type Faraday Cage (TTFC). The device was deployed in two field campaigns at Sakurajima volcano (Japan, November 2023) and Etna volcano (Italy, July 2024). At Sakurajima, charges ranging from 0.5 to 150 pC and settling velocities of 0.1 to 5 m/s were detected, with aggregates observed in deposits despite low explosive activity. In contrast, no charges or aggregates were observed at Etna during high-intensity paroxysmal explosions. Differences in fragmentation, grain size distribution, or atmospheric conditions may explain this discrepancy. The device was also used in preliminary laboratory experiments focusing on the collision and eventual sticking of charged particles, proving its utility in both field and laboratory settings.